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Tug Technology & Business

Owners lured by prospect of mix and match propulsion

Wed 01 May 2019 by Gavin Lipsith

Owners lured by prospect of mix and match propulsion
Planetary gearing allows users of Caterpillar's AVD to optimise propeller speed independently of engine speed

From reducing engine installations to adding an ice-breaking boost of power, tug operators continue to appreciate the adaptability of hybrid propulsion configurations

A harbour tug with a new hydraulic hybrid propulsion system is to be built by Sanmar Shipyards to a Robert Allan design. The tug will be fitted with Caterpillar Marine’s advanced variable drive (AVD) system. First developed in 2017 but yet to be applied in the tugboat sector, this allows operators to optimise propeller speed independently of engine speed while controlling distribution of power among propulsion components.

The new tug design is based on the proven RAmparts 2400-SX design, with modifications for the AVD system. Boğaçay 38 has been optimised for harbour tug operations with 70 tonnes of bollard pull and Fi-Fi 1 firefighting capability. Propulsion equipment includes Caterpillar 3512C main engines, Caterpillar MTA627 azimuthing thrusters, and a C32 auxiliary engine powering the hybrid hydraulics as well as the Fi-Fi pump.

Robert Allan was retained by Caterpillar Marine to support and advise on applying the new AVD technology for hybrid tug applications. This led to the debut tugboat project. Construction is currently under way with delivery scheduled for later in 2019.

The AVD system differs from a typical power take-in solution by incorporating a planetary gear set which allows seamless clutch engagement of main engines, auxiliary engines, or both. This allows propeller speed independent of engine speed so optimal engine efficiency can be achieved. Caterpillar claims this can lead to fuel savings of 15-20%, offering the benefits of diesel-electric propulsion at a lower cost and smaller footprint.

As a direct result of the AVD system, main engines can be downsized in most applications, with supplemental power provided by auxiliary engines. The system also provides inherently high levels of propulsion redundancy.

Removable bow

A Finnish project is set to offer the capability for almost any tug to be used as an icebreaker thanks to a removable bow. The Finnish Transport Infrastructure Agency is launching a new icebreaker concept equipped with the motorised bow. As an initial trial, an icebreaker ferry will be moored in Mustola harbour in Lappeenranta and will operate in the Lake Saimaa area from late 2020.

The removable bow, to be delivered by Turku Repair Yard, is part of the Winter Navigation Motorways of the Sea II project – a €7.6M (US$8.6M) scheme, co-funded by EU Connecting Europe Facility programme which aims to develop and improve the safety of winter navigation. One of its key targets is creating a motorised icebreaking removable bow concept, which will enable ice-strengthened vessels to be used as icebreakers.

“Lake Saimaa’s ice is more solid than sea ice and can reach up to 80-cm thick,” says Finnish Transport Infrastructure Agency project operator Jukka Väisänen. “Developing this innovative design concept for the removable bow and equipping it with its own propulsion system means we will achieve savings in capital costs, as we will charter the pusher for only part of the year. We are also expecting to see savings in fuel consumption thanks to the hybrid propulsion system.”

Danfoss Editron’s hybrid-electric system will power the removable bow with two generators configured as a DC system and two propulsion systems. A front supercapacitor will allow peak power demands to be controlled, while Editron software cuts fuel consumption by enabling diesel generators to be driven at variable speeds. The power plant and propulsion can be operated from the pusher tug wheelhouse and the machinery can operate unmanned.

“This new kind of removable bow will make the whole industry more efficient and sustainable, as it enables virtually any kind of tug to become an ice-breaker ship,” says Danfoss Editron project manager Kari Savolainen.

Ice service is unlikely to be a consideration for a new environmental tugboat set to become the first IMO Tier III compliant tugboat in the Mediterranean. P&O Reyser has ordered a 27-m harbour tug from Drydocks World Dubai shipyard in the UAE. It will be built to Lloyd’s Register class and will be the first tugboat reference for MAN Energy Solutions’ MAN 175D engine.

The asymmetric tractor tug (ATT) will provide 75 tonnes of bollard pull, with propulsion provided by fixed pitch propeller azimuth thrusters. It will be built to a Cintranaval CND-17009 Eco Silent design. P&O Reyser – which provides towing, mooring and auxiliary services in 11 Spanish ports with a fleet of more than 100 vessels in service – expects the ATT to enter service in the Port of Barcelona from mid-2020.

MAN Energy Solutions will supply two MAN 12V175D MM engines, each rated at 2,220 kW, with selective catalytic reduction (SCR) after-treatment systems. According to MAN Energy Solutions head of four-stroke marine sales Lex Nijsen, the engines were selected because of their “compact footprint, fuel-efficient performance and the flexible design approach taken with the SCR layout”.

Over the past 30 years MAN has supplied 592 engines for tugs covering a range of different engine types, with the most frequent being the MAN 27/38 engine.

Meanwhile Finnish thruster specialist Steerprop has also found a debut application for what it describes as a new ‘workboat series’. The SP 25 W D unit’s lower housing is made of cast steel, compared to the standard SP 25 D housing of separate moulded and welded steel parts. Other structures including nozzles also feature improved designs compared to the company’s previous range.

Two new multipurpose vessels being built by Remontowa Shipbuilding under contract from Szczecin Maritime Authority will be the first to deploy Steerprop’s W-series propulsion units. Steerprop will supply two propulsion unit ship sets, each including a pair of Steerprop SP 25 WD propulsion units with a control system.

A flexible diesel-electric propulsion system will give the 60-m vessels good manoeuvrability and dynamic positioning performance. They will offer a deadweight capacity of 350 tonnes and a bollard pull of 40 tonnes at 15 knots, suited to the workboats’ emergency towing requirements.

The new vessels will be used for key statutory tasks for Poland’s maritime authorities in the ports of Szczecin and Gdynia, replacing two ageing buoy tenders in use since 1982. Their service will mainly include inspection, maintenance, transportation and replacing navigational buoys. The vessels will also be fitted for hydrographic tasks. In case of emergencies at sea, they will be capable of emergency response, including towing operations, oil spill recovery, firefighting and other search-and-rescue tasks.

Both vessels will feature high ice-breaking power. These will be the first Steerprop products to receive Polish Register of Shipping (PRC) classification. With PRS L1 ice class, the vessel will be a new category for the class society.

Both vessels are expected to be ready for service by June.

Design enhancements to Schottel’s azimuth thrusters will receive their first reference on a newbuild escort and harbour tug being built for US tug operator McAllister Towing at Washburn & Doughty shipyard in Maine. It will be equipped with two SRP 490 rudderpropeller azimuth thrusters with an input power of 2,525 kW each (at 1,800 rpm), delivering an expected bollard pull of about 82 tonnes.

Schottel’s rudderpropellers have undergone several technical updates. Recently added features include enhanced corrosion protection anodes, high-torque gear technology and high-performance nozzles. More than 1,000 units of types 490 and 460 have been sold since the first thrusters were delivered in 1999, and the company has delivered more than 70 azimuth thrusters to McAllister alone.

Main propulsion consists of two Caterpillar CAT 3516 engines, each driving an SRP 490 azimuthing stern drive unit with fixed pitch propellers 2,800 mm in diameter. The configuration enables a free running speed of more than 14 knots. The ASD-type tug is designed for harbour and terminal operations as well as for coastal towing.


Longer engine life boosts retrofit case for US workboats

US workboat engines are used for more than twice as long as previously estimated, enhancing the benefits of retrofitting engines, according to new research.

The study, for enginebuilder consortium Diesel Technology Forum (DTF) and ecological lobby group Environmental Defense Fund, found that workboat engines have a service life of around 50 years, compared to the 23 years used by the US Environmental Protection Agency (EPA) to set its emissions reduction targets.

A longer service life means that older engines are replaced more slowly, resulting in 57% lower NOx reductions each year than those forecast by EPA. But it also increases the potential impact of installing new technology, DTF said, as upgraded engines will have a longer period in which to reduce emissions.

The groups are urging US states to repower vessels with more modern, cleaner engine technology. States can receive funding for repowering commercial workboats to reduce NOx under the US$2.9Bn environmental mitigation trust established by Volkswagen Group in the wake of the emissions test fixing scandal in 2015.

“Large engine repowers are more cost effective on a dollar-per-tonne-of-emissions-reduced basis than other projects, which should make for an easy and compelling choice for states,” said DTF executive director Allen Schaeffer. “The incentive funds give operators a brand new, more efficient, fuel-saving and lower-emitting engine at a fraction the cost. Even better, the emission benefits associated with these projects will accrue quickly and persist for many years.”

The study, conducted by Ramboll Environ, looks at engines with a cylinder displacement of 5-30 litres – loosely equivalent to a maximum power output of around 8 MW – classed as ‘category two’ engines by EPA. New marine diesel engines used have been required to meet EPA Tier 4 emissions standards since 2015. But DTF said that the cost and downtime required to upgrade to new engines have likely delayed investments in the newest technologies.


MOL takes delivery of gas-fuelled tug

Mitusi OSK Lines (MOL) took delivery of its first dual-fuelled tugboat, Ishin, on 27 February. The 43.6-m, 250-gt vessel was built by Kanagawa Dockyard Co. It will be operated by MOL group company Nihon Tug-Boat Co. The LNG fuel was supplied by Osaka Gas Co using truck bunkering in Sakai Senboku port.

Leveraging its high-speed performance, with capability in excess of 16 knots, Ishin will escort large freighters during port calls. The tug is powered by two 6EY26DF dual-fuel engines manufactured by Yanmar. It features a removable LNG fuel tank mounted on the exposed deck at the stern of the ship, which offers simplicity for bunkering, maintenance and inspection.

MOL has worked closely with the Osaka prefecture’s port and harbour bureau and Osaka Gas to develop an LNG fuel supply system for ships in Sakai Senboku Port. This is the first LNG supply infrastructure in Osaka Bay.

MOL established a bunker business division in 2017 to accelerate LNG initiatives. It aims to widen the use of LNG fuel for ships and workboats.

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